Microtube heat exchanger devices, systems and methods

ABSTRACT

A microtube heat exchanger is disclosed, including two end plates with an array of holes or openings and an array of microtubes disposed in the array of openings between the two end plates. The heat exchanger can be used in environmental control systems, including systems for aerospace applications.

PRIORITY CLAIM

This application claims priority to U.S. Provisional Application No.62/972,836 filed on Feb. 11, 2020.

FIELD OF THE TECHNOLOGY

The present technology relates to microtube heat exchangers for use inaerospace and more particularly to the manufacture and use of microtubeheat exchangers in environmental control systems, including foraerospace.

BACKGROUND OF THE TECHNOLOGY AND RELATED ART

Environmental control systems are used in aerospace applications to coolor heat aircraft systems and human occupant compartments. Examplesystems in which an environmental control system is used includeelectronic systems such as avionics, radar, electric power systems,accessory electronics for mission needs, and the like, as well asmechanical systems such as engine cooling, hydraulic cooling, enginebleed air cooling, among others. This is accomplished by heating orcooling of fluids, typically air or a liquid coolant. Traditionally,efficiency requirements and limitations in technology control theminimum size of heat exchangers required for certain systems. Forexample, various aerospace applications may require refrigerant to air,refrigerant to liquid, liquid to liquid, air to liquid, or air to aircooling to expel heat from various components of the system. A heatexchanger, sometimes referred to as a condenser or evaporator, is usedin such systems, including environmental control systems.

As aerospace applications of environmental control systems continue todemand more efficient systems with smaller size requirements undercontinuously increasing thermal loads with increasing number of systems,there remains a need for improved heat exchangers.

BRIEF DESCRIPTION OF THE DRAWINGS

The present technology will become more fully apparent from thefollowing description and appended claims, taken in conjunction with theaccompanying drawings. Understanding that these drawings merely depictexemplary aspects of the present technology, they are therefore not tobe considered limiting of its scope. It will be readily appreciated thatthe components of the present technology, as generally described andillustrated in the figures herein, could be arranged and designed in awide variety of different configurations. Nonetheless, the technologywill be described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

FIG. 1 is a schematic of a system in accordance with one aspect of thetechnology;

FIG. 2 is a top perspective view of a heat exchanger core in accordancewith one aspect of the technology;

FIG. 3 is a detailed top view of the heat exchanger core of FIG. 2 ;

FIG. 4 is an inside perspective view of a heat exchanger end plate inaccordance with one aspect of the technology, while in the middle ofbeing built;

FIG. 5 is a front view of another heat exchanger end plate in accordancewith one aspect of the technology;

FIG. 6 a is front view of a heat exchanger core in accordance with oneaspect of the technology;

FIG. 6 b is a side view of the heat exchanger core of FIG. 6 a;

FIG. 7 is a perspective view of an array of microtubes according to oneaspect of the technology;

FIG. 8 is a perspective view of an array of microtubes in accordancewith another aspect of the technology;

FIG. 9 is a microtube heat exchange system in accordance with one aspectof the technology;

FIG. 10 a is an isometric view of the microtube heat exchanger of thesystem of FIG. 9 ;

FIG. 10 b is a cutaway view of the microtube heat exchanger of thesystem of FIG. 9 ;

FIG. 11 is an end isometric cutaway view of the microtube heat exchangerof the system of FIG. 9 ;

FIG. 12 is a cutaway view of the microtube heat exchanger of the systemof FIG. 9 ;

FIG. 13 is a diagram of airflow in the system of FIG. 9 ;

FIG. 14 is a front cutaway view of the system of FIG. 9 ;

FIG. 15 is another example of the system of FIG. 9 ;

FIG. 16 is a detailed view of the microtube heat exchanger of the systemof FIG. 15 ;

FIG. 17 a is a side perspective view of a heat exchanger in accordancewith one aspect of the technology;

FIG. 17 b is a side perspective view of a system incorporating themicrotube heat exchanger of FIG. 17 a in accordance with one aspect ofthe technology;

FIG. 18 is a schematic of a system in accordance with one aspect of thetechnology using the microtube heat exchanger of FIGS. 17 a -b;

FIG. 19 is a top cross-sectional view of a microtube heat exchanger inaccordance with one aspect of the technology;

FIG. 20 is an isometric view of the heat exchanger core of FIG. 19 ;

FIG. 21 is a front view of the heat exchanger core of FIG. 19 ;

FIG. 22 is a side view of the heat exchanger core of FIG. 19 ;

FIG. 23 is a schematic of a system in accordance with one aspect of thetechnology using the microtube heat exchanger of FIGS. 19-22 ;

FIG. 24 is a cross-sectional view of an in-line arrangement ofmicrotubes in accordance with one aspect of the present technology;

FIG. 25 is a cross-sectional view of an offset arrangement of microtubesin accordance with another aspect of the present technology;

FIG. 26 is a perspective view of a sheet of microtubes according to oneaspect of the technology;

FIG. 27 is a cross-sectional view of another arrangement of microtubeswithin a microtube heat exchanger according to one aspect of the presenttechnology;

FIG. 28 is a perspective view of the microtubes within a microtube heatexchanger of FIG. 27 ;

FIG. 29 is a cross-sectional view of another arrangement of microtubesaccording to an aspect of the present technology;

FIG. 30 is a perspective view of the microtubes of FIG. 29 ;

FIG. 31 is another perspective view of the microtubes of FIG. 29 ;

FIG. 32 is a cross-sectional view of an arrangement of microtubes inaccordance with another aspect of the present technology;

FIG. 33 is a perspective view of the arrangement of microtubes of FIG.32 with and illustration of how the varying angle can change thedirection of the cross flow fluid;

FIG. 34 is a perspective view of a heat exchanger using the arrangementof microtubes of FIG. 32 ;

FIG. 35 is a chart illustrating the arrangement of microtubes of FIG. 32;

FIG. 36 is another chart illustrating the arrangement of microtubes ofFIG. 32 ;

FIG. 37 is a cross-sectional view of yet another arrangement ofmicrotubes according to aspects of the technology;

FIG. 38 is a cross-sectional view of an arrangement of microtubesaccording to other aspects of the technology;

FIG. 39 is a perspective view of the microtubes of FIG. 38 ;

FIG. 40 a is an end view of a microtube heat exchanger core according toother aspects of the technology;

FIG. 40 b is a side view of the microtube heat exchanger core of FIG. 40a;

FIG. 40 c is an annotated end view of the microtube heat exchanger coreof FIG. 40 a;

FIG. 41 is an end view of another microtube heat exchanger coreaccording to aspects of the technology;

FIG. 42 a is a perspective view of a microtube heat exchanger coreincluding foreign object debris or damage protection according toaspects of the technology;

FIG. 42 b is a partial cross-sectional view of the microtube heatexchanger core of FIG. 42 a;

FIG. 43 a is a perspective view of another microtube heat exchanger coreincluding foreign object debris or damage protection according toaspects of the technology;

FIG. 43 b is a partial cross-sectional view of the microtube heatexchanger core of FIG. 43 a;

FIG. 43 c is a detailed view of the microtube heat exchanger core ofFIG. 43 b.

DETAILED DESCRIPTION

The following detailed description of exemplary aspects of thetechnology makes reference to the accompanying drawings, which form apart hereof and in which are shown, by way of illustration, exemplaryaspects in which the technology may be practiced. While these exemplaryaspects are described in sufficient detail to enable those skilled inthe art to practice the technology, it should be understood that otheraspects may be realized and that various changes to the technology maybe made without departing from the spirit and scope of the presenttechnology. Thus, the following more detailed description of the aspectsof the present technology is not intended to limit the scope of thetechnology, as claimed, but is presented for purposes of illustrationonly and not limitation to describe the features and characteristics ofthe present technology and to sufficiently enable one skilled in the artto practice the technology. Accordingly, the scope of the presenttechnology is to be defined solely by the appended claims.

The following detailed description and exemplary aspects of thetechnology will be best understood by reference to the accompanyingdrawings, wherein the elements and features of the technology aredesignated by numerals throughout.

The present technology includes an improved heat exchanger for use inaerospace systems. In just one embodiment, the improved heat exchangeris used in an environmental control systems (ECS), however otherapplications will be discussed and contemplated herein. To provide thisheat rejection issue in the aerospace industry, the efficiency of theheat exchanger must be increased. This present technology includes useof a micro-tube style heat exchanger to reject or absorb heat in anaerospace environment on board of new and existing aircraft and aircraftpod applications. The microtube heat exchangers can be of any size andshape of which an array of tubes is utilized as the method oftransferring heat from one fluid to another. In one aspect of thetechnology, the tubes are individual hollow tubes, such as cylindricaltubes with a circular cross section, or tubes having other crosssections such as square, triangular, oval or elliptical, that areconverted from an individual state and built into one unit as a devicecalled a micro-tube heat exchanger. The heat exchanger may be across-flow device, or it may be a parallel-flow or counter-flow device.The microtube heat exchanger is built such that the entire array ofthousands, but not limited to thousands, of micro-tubes is held togetheras one structure and acts as one single component in the aircraftsystem. The microtube heat exchanger consists of an array of tubes thatpasses either a water or oil based liquid, 2-phase refrigerant, or gasthrough the center of the tubes, and allows either a gas or a water oroil based liquid to cross over the tubes in cross-directional flow, orin a parallel flow or a counter flow, depending on the application, tocomplete the heat exchange with the fluid travelling down the center ofthe tubes.

In other aspects of the technology, the addition of a microtube heatexchanger to an aircraft ECS system allows for greater heat exchangethan previously capable. The fluid used as a coolant passes through apump or boosting pump, and instead of passing through a traditional heatexchanger, the present system incorporates a microtube heat exchangerimproving the efficiency of the system. The fluid then continues throughto the aircraft equipment and returns to the ECS expansion tank. Themicrotube heat exchanger systems of the present technology allows formore compact and efficient heat exchange than existing ECS and heatexchange systems. In addition to increasing the efficiency of heatexchange, adding a microtube heat exchanger to a heat exchange system,such as an aircraft ECS, allows other components of the system to bemore efficient. For example, the efficiency of the microtube heatexchanger in an aircraft ECS allows for less demand on the compressorand pump in the ECS. The decreased demand allows for reductions in sizeand weight of the components, which advantageously allows for furtherreductions at the system level

The aspects of the technology discussed herein are applicable to avariety of systems in the aerospace industry, including allenvironmental control systems in the aerospace industry. As discussedabove, the present technology is also applicable to all aircraft, allaircraft systems, which includes all environmental control systems andall accessory aircraft systems including roll on equipment and weaponssystems, especially direct energy weapons, and all aircraft pod systemsin an aerospace environment The present technology can also beapplicable to an array of customers across aerospace applications andother industries.

Throughout this disclosure, the terms microtube heat exchanger andmicrotube heat exchanger core may be used interchangeably. It isunderstood that the microtube heat exchanger cores depicted anddescribed in the present technology may be employed in any standardmicrotube heat exchange system. In one aspect of the technology, amicrotube heat exchanger uses a microtube heat exchanger core in theplace of a traditional heat exchanger core. It is also understood thatthe present technology relates to retrofitting existing systems toreplace a traditional heat exchanger with a more efficient microtubeheat exchanger, and that it also relates to new heat exchange systemsincorporating microtube heat exchangers having microtube heat exchangercores.

As used herein, the term “liquid” will be understood to reference afluid in liquid form, but shall not limit the present technology to anyother form a fluid. In other words, the microtube heat exchangers of thepresent technology may be used in any fluid application, includingliquids, gases or plasmas. It has been found that there is a thresholdof tube diameter such that when the tube diameter gets small enough, theefficiency of an array of those tubes can be greater in both “heattransfer per pound” or “heat transfer per volume” than existing methods.

The present technology is applicable to, and is intended to beapplicable to all systems for all aircraft, which includes all aircraftenvironmental control systems, all accessory aircraft systems includingroll on equipment and weapons systems, especially direct energy weapons,and all aircraft pod systems in any aerospace environment. Aspects ofthe technology can also be applicable to other users. In other words,the microtube heat exchanger of the present technology can be used inany aerospace system requiring a heat exchanger. For example, themicrotube heat exchanger can be used in environmental control systems,such as occupant cooling/heating, avionics cooling, auxiliaryelectronics cooling, auxiliary equipment cooling such as pods, engineoil cooling, transmission oil cooling, and auxiliary power unit cooling.Any of these systems may be vapor cycle systems involving two-phaserefrigerant, air cycle systems involving single phase bleed-air drivencooling systems, passive liquid systems involving a single phase liquid,and passive gas systems involving a single phase gas, such as air. It isalso be understood that the present technology relates to additionalrelevant aerospace systems, including systems on aircraft and systems onspacecraft.

With specific reference now to FIG. 1 , FIG. 1 is a general a schematicfor a microtube heat exchange system 100 in accordance with one aspectof the technology. The heat from a coolant is ejected into the air thatflows through the microtube heat exchanger 110. This system may be anenvironmental control system that utilizes microtube heat exchangers ina cross-flow, annular radiator configuration. Such systems are highlyefficient, with small sizes and low pressure drops.

At the most basic level, a microtube heat exchange system includes amicrotube heat exchanger, which includes a heat exchanger core usingmicrotubes. One example of a microtube heat exchanger core is shown inFIGS. 2-3 .

In aspects of the present technology, the microtube heat exchanger coreincludes at least a first end plate 220 and second end plate 230, eachend plate having an array of openings 225. In other examples, one ormore mid plates 240 may be disposed within the heat exchanger. Theexchanger also includes an array of microtubes 250 disposed between thefirst and second end plates. The microtubes can be laser welded to theend plates. In other examples, the microtubes are attached by way ofother means developed for precisely joining two very small elements suchas the microtubes and the openings. For example, other means may includebrazing or soldering. In aspects of the technology, the microtubes 250and end plates 220, 230 make up a heat exchanger that is installed in aheat exchange system that is installed in an aerospace application. Themicrotubes and end plates can be stainless steel, with the microtubeslaser welded to the end plates, as discussed herein. In other aspects ofthe technology, the microtubes and end plates can be any metal suitablefor aerospace, including steel, aluminum, brass, or any allows thereof.

As further depicted in FIGS. 2-3 , in one aspect of the technology thearray of openings 225 in the end plates form straight longitudinal rowsparallel to the direction of fluid flow and straight transverse rowsnormal to the direction of fluid flow. In yet other examples, asdiscussed herein, the array of openings in the end plates form staggeredlongitudinal and transverse rows.

The microtube heat exchanger according to aspects the present technologycan include an array of microtubes forming a cylinder, a rectangle, orany other shape, such as a square, an arc, a curve, or a horse-shoeshape. The specific dimensions of the arrangement of microtubes can becustomized to fit any application, including customization based on thesize or footprint requirements, and also customization based on the flowproperties and requirements.

In aspects of the technology, the microtube heat exchanger is installedin an aerospace heat exchange system such as an environment controlsystem. For example, the environmental control system can include afirst fluid flowing through the inside of the array of microtubes andsecond fluid flowing across the outside of the array of microtubes.

The microtube heat exchanger in one aspect of the present technology caninclude specific ratios of the diameter of each microtube compared tothe spacing between the tubes, either in the longitudinal spacing, orthe transverse spacing, as further described and depicted in FIGS. 34-35. In some aspects of the present technology involving in-linearrangements of microtubes, the ratio of the diameter of the tube to thelongitudinal spacing between the centers of each tube is 1.25. In otheraspects, the ratio can be between 1 and 5.0. In yet other aspects, arange between 1 and 20 may be used. In some aspects of the technology,the ratio of the diameter of the tube to the transverse spacing betweenthe centers of each tube is 2.75. In yet other examples, the spacing canbe between 2.0 and 10.0. And again, in other aspects, a range between1.01 and 20 may be used. Now with reference to off-set arrangements ofmicrotubes, the ratio of the diameter of the tube to the longitudinalspacing between the centers of each tube can be 1.3. In other examples,the ratio can be between 1.01 and 10.0, or can be between 1.01 and 20.In the same off-set arrangements, the ratio of the diameter of the tubeto the transverse spacing between the centers of each tube can be 1.5,or in other examples between 1.01 and 10.0, or can be between 1.01 and20. It will be understood by those of ordinary skill in the art based onthe present technology that other ratios are contemplated and may beapplicable to specific situations based on the properties andrequirements involved.

In aspects of the technology, the microtubes for use in the microtubeheat exchangers are cylindrical microtubes having circular crosssections. In yet other examples, as disclosed herein, other crosssections and shapes of tubes can be used. When cylindrical microtubesare used, a tube size of 0.010 inches to 0.080 inches at the outerdiameter can be used. The tube wall thickness may range between 0.0005inches and 0.010 inches. The tube length can range between 0.5 inchesand 240 inches. The overall heat exchanger width can range between 0.5inches and 240 inches, and the depth of the heat exchanger, or in otherwords one row of tubes, can range between 0.012 inches and 24 inches.The present technology will make it clear to those of ordinary skill inthe art the variations hereof that are applicable and covered by thepresent disclosure.

In other aspects of the technology, a heat exchange system, such as avapor cycle system, air cycle system, passive liquid or gas system, isdisclosed including a microtube heat exchanger having two end plates,each having an array of openings. The exchanger also includes an arrayof microtubes disposed between the two end plates, where the microtubesare laser welded to the end plates. In aspects of the system, a firstfluid travels through the microtubes of the heat exchanger and a secondfluid contacts the outside of the microtubes. In aspects of thetechnology, the vapor cycle system is configured and adapted for use inaerospace.

As further discussed herein, the array of microtubes can form straightlongitudinal rows parallel to the direction of fluid flow and straighttransverse rows normal to the direction of fluid flow. In other examplesof the system the array of microtubes can form staggered longitudinaland transverse rows. The array of microtubes can form one of a cylinder,rectangle, a square, an arc, a curve, or horse shoe shape. In yet otherexamples, any geometrical configuration can be formed by the array ofmicrotubes.

According to some aspects of the technology, the array of microtubes 250are aligned with the array of openings 225 as shown in FIG. 4 . Portionsof the microtubes 250 are shown in arrangement on an end plate 220. Theend plate 220 may include an arrangement of holes or openings 225, whichmay take the form of a pattern. In some aspects of the technology, thepattern of the holes 225 in the end plate is arranged to reduce thesurface area of the end plate, minimizing the resistance that the endplate causes to flow of the liquid into the microtubes. In other aspectsof the technology, the arrangement of the openings 225 in the end plateis chosen based on the external flow characteristics desired, or inother words, to arrange the microtubes for specific applications basedon the external fluid that will flow over the outside of the microtubes,as described more fully herein.

Another example of a microtube heat exchanger 310 is depicted in FIG. 5. The end plate 320 of the microtube heat exchanger 310 is shown, withthe pattern of holes or openings 325 leading to microtubes (not shown)behind the end plate 320. In this example, the holes are arranged in anoffset or staggered pattern, as described with reference to FIGS. 34-35.

FIGS. 6 a-6 b show a microtube heat exchanger core 410 in accordancewith one aspect of the present technology. The heat exchanger 410includes an array of microtubes 450 arranged in a cylindrical shape witha first end plate 240 on one end and a second end plate 430 on anotherend. A fluid, such as a coolant or other liquid, flows through the tubeswhile another fluid, such as a liquid or gas, in most cases air, flowsacross the tubes to effectuate the heat exchange. Such a heat exchangercan be used in single phase or dual phase systems. A fluid pump can beused in such systems to keep the fluid flowing within the tubes,separate from the fluid flowing across the tubes. As shown in FIG. 6 aby the array of openings 425, the array of microtubes 450 includesthousands of microtubes that are welded to the end plates 420, 430. Insome examples, the microtubes 450 are laser welded to the end plates420, 430 as described herein. In other aspects of the technology, themicrotubes may be cast or 3D printed together with the end plates.

FIGS. 7-8 show yet another heat exchanger microtube array exampleaccording to aspects of the technology. The microtubes may be arrangedin a rectangular heat exchanger, in contrast to the cylindrical heatexchangers previously discussed. The rectangular heat exchanger includesthousands of microtubes arranged in rows and columns, each welded to anend plate on each end which then forms the microtube heat exchanger. Aspreviously discussed, a fluid within the tubes is cooled as anotherfluid runs across the tubes.

FIGS. 9-16 depict a microtube heat exchanger for a single phase, liquidto air fan system in one aspect of the technology. The microtube heatexchanger is in a “horseshoe shape,” with an array of microtubes havinga liquid header on each end of the tubes (or maybe we say end plates?Since so much of the text says end plates). Liquid flows through thetubes, the two fans pull or push the air out of the center of thehorseshoe, and heat is exchanged from the liquid to the air. Forexample, cold air may be extracted from the environment by the airflowcreated by the fans. The cold air may pass through the microtubes in thehorseshoe arrangements, transferring heat from the liquid inside thetubes to the air. The fans then pull the hot air out of the center ofthe heat exchanger. The horseshoe shaped heat exchanger may be used aspart of a system as shown in FIGS. 14-16 , where the heat exchanger sitsatop a cabinet that may include the various components of theenvironmental control system, as disclosed herein.

FIGS. 17 a-b show a heat exchanger and an air fan setup, respectively,for a liquid to gas heat exchange system using fan induced flow for thegas. The microtube heat exchanger may be a full cylindrical design withan array of microtubes attached at liquid headers on each end of thetubes. In some examples, liquid flows through the tubes for the liquidheat exchange, and a gas flows across the tubes from the forced movementfrom a fan on each end of the cylinder for the gas heat exchange, asshown in FIG. 17 b . The fans can either pull the air out of the centerof the heat exchanger, or in some embodiments the fans can push the airinto the center of the heat exchanger forcing the gas to expel out ofthe cylinder across the microtubes and achieve the same result. Theoperation of the heat exchanger of FIGS. 17 a-b is similar to theoperation of the horseshoe-shaped heat exchanger discussed above.

FIG. 18 is a schematic for the single phase, liquid to air fan inducedsystem shown in FIG. 17 . The airflow induced by the fans cools the hotliquid in the tubes of the heat exchanger. The hot liquid, which may bea coolant, exits the system in its cooled state, and coolant enters thesystem at the coolant return in its hot state. In some embodiments theliquid can be cool entering into the heat exchanger, and exchange heatwith a hot gas entering the cross-flow of the heat exchanger where theliquid exits the heat exchanger hot and the gas exits the heat exchangercool achieving the same results. In some embodiments the liquid passingthrough the heat exchanger can be a refrigerant that realizes a phasechange, making the liquid a 2-phase circuit such as a refrigerant wouldreact as the liquid instead of a coolant.

FIGS. 19-22 depict a microtube heat exchanger 810 in accordance withaspects of the present invention. The heat exchanger 810 may be used ina single phase cooling system for liquid to air heat exchange based onram air. The heat exchanger may be used in high velocity applications,such as military jets, including pod applications. The exchangerincludes stacks of microtubes 850 arranged as shown in FIG. 22 d . Thestacks are angled for optimum airflow, and include mid plates 840 orstiffener plates to support the microtubes. In one aspect of thetechnology, cold RAM air comes in through inlet scoops from forwardmovement of an aircraft, such as a jet. The air passes across themicrotube heat exchanger, which has hot liquid running through thetubes. The cold air cools the hot liquid in the tubes, and hot air exitsout the back of the aircraft.

In aspects of the technology, the mid plates 840 can include multiplemid plates. The mid plates may provide structural strength, vibrationdampening, or vibration node changing, harmonic vibration altering. Insome aspects, the mid plates 840 may be angled mid plates, such that theflow of the fluid passing over the heat exchanger can be directed by themid plates. For example, in FIGS. 19-21 , the mid plates may be angledto force the flow of RAM air that is normal or perpendicular to the longaxis of the heat exchanger when it enters the heat exchanger to exit atan angle that is not perpendicular or normal to the long axis of theheat exchanger.

In other aspects of the technology, the mid plates can be used to directthe flow of fluid on the exterior of the head exchanger even withoutangling the mid plates. For example, in may heat exchange systems, theexterior fluid arrives to the heat exchanger through a duct and exitsthrough a duct. The duct leading to the heat exchanger most oftenincludes a turn, a bend or an angle, such that the fluid arriving to theexterior of the heat exchanger is not uniform, but rather isconcentrated on one end while the other end is starved of the fluidbased on the ducting. The mid plates or cross plates, though parallelrather than angled, can be staggered in such a way that they direct theexterior fluid to flow more evenly across the heat exchanger. Forexample, where the exterior fluid is highly concentrated based on theentry ducting, mid plates can be staggered more densely to provide addedresistance to flow that will redirect the flow of the exterior fluid toother parts of the heat exchanger.

FIG. 23 shows in detail the schematic for a single phase, liquid to airheat exchange system shown in FIG. 1 . The system is an example of ramair style heat exchange. In some aspects, the system includes two heatexchangers, each with a separate inlet for ram air, and a single outletfor hot air after heat exchange. In other aspects, other configurationsof heat exchangers, inlets and outputs may be used. As discussed herein,the heat exchanger of this system can include microtube heat exchangers.The heat exchangers of FIG. 23 can be the microtube heat exchanger ofFIGS. 19-22 . In some embodiments the liquid passing through the heatexchanger can be a refrigerant that realizes a phase change, making themicrotube heat exchangers a 2-phase circuit such as a refrigerant wouldreact as the liquid instead of a coolant.

FIGS. 24-25 show examples of arrangements of the microtubes 1650 of theheat exchanger of the present technology. In some examples, themicrotubes are arranged “in-line” as shown in FIG. 24 . In otherexamples, the microtubes are arranged in a “staggered” formation asshown in FIG. 25 . Choice of in-line or staggered is dependent uponshell-side (outside of tubes) fluid properties, primarily driven byfluid Prandtl number. In-line banks are chosen for low Prandtl numbers(air for example), staggered is chosen for high Prandtl number fluids(liquid coolants, oils, etc.).

The diameter of each microtube, or the tube size, is driven by tube-side(inside the tubes) fluid properties. In general, smaller tube sizeresults in more efficient heat transfer, however minimum size is limitedby pressure drop properties of the fluid passing through the inside ofthe tubes. In some aspects, a 0.022″ OD, 0.002″ wall thickness tube maybe standard for most coolants (PAO, EGW, PGW, water) and refrigerants(R134a, R22, R404c, etc.). For higher viscosity fluids (turbine engineoils, transmission oils, gearbox oils, etc.) a 0.0355″ OD tube with0.002″ wall thickness may be desirable. This larger diameter allows foran acceptable pressure drop with the more viscous fluids.

In choosing an arrangement of microtubes, tube spacing or the distancebetween each microtube is chosen for each application. In manyapplications, tube spacing is used to optimize the performance of themicrotube heat exchanger. Spacing is often tailored to particularapplications depending on fluid type, flow rates, pressure drop vs. sizetrades, pressure drop limitations, size limitations, etc. However, somestandards are desirable in some situations. For example, tubelongitudinal and transverse spacing is defined by S_(L) and S_(T)parameters respectively, which are ratios of tube spacing (center tocenter) to tube diameter D. Longitudinal is parallel to fluid flow whiletransverse is normal to fluid flow. In some examples, the standardspacing for in-line tube arrangements is a ration of D to S_(L) of 1.25and a ration of D to S_(T) of 2.75. For staggered arrangements ofmicrotubes, the standard ratios can be, respectively, 1.3 and 1.5.Nevertheless, as discussed in more detail herein, the ratios may beanywhere between 1.01 and 4.0, or higher, depending on the specificapplications.

Tube wall thickness is driven by environmental and operationalrequirements. From a thermal performance perspective, the goal is tohave the thinnest wall possible as this this minimizes conductivethermal resistance. In some examples of the present technology, atypical wall thickness for the microtubes in heat exchangers is 0.002″.

When driven by high pressure applications (>1000 psig), thicker wall isrequired. When severe foreign object debris (also known as FOD) orsand/dust requirements are applied, several rows on the inlet side ofthe heat exchanger are sized with thicker walls to resist damage due toparticle impact.

In yet other examples of the present technology, an array of microtubes1710 for a heat exchanger core may form a sheet of microtubes 1750, asdepicted in FIG. 26 . The sheet of microtubes 1750 may have nearly thesame outside surface area as an array of microtubes, while retainingsome benefits. In such examples, an end plate may include an array ofslots the size of the sheets, rather than much smaller and greaternumber of openings for each microtube. Such an arrangement may furtheroptimize the laser welding process. A heat exchanger incorporating asheet of microtubes may also direct the travel of fluid on the outsideof the heat exchanger with greater consistency.

FIGS. 27-28 depict another example of an array of microtubes 1850 forheat exchanger core 1810 in accordance with the present technology. Themicrotubes 1850 may have a triangular cross-section. Yet other exampleswill be understood to apply to the present technology, including squareor rectangular cross sections of microtubes, or any form of oval orelliptical cross-sectional shape.

FIGS. 29-31 depicts another example of an array of microtubes 1950 for amicrotube heat exchanger core 1910 according to the present technology.The microtubes 1950 can include an elliptical cross-sectional shape andbe formed in a staggered or offset configuration.

In yet other examples, the microtube array according to the presenttechnology can include an arrangement whereby the microtubes are offsetsuch that they direct the flow of the fluid on the outside of the heatexchanger. For example, whether circular, rectangular, square,triangular, oval, or elliptical cross-sections of tubes are used, rowsof microtubes may be gradually offset to direct the flow of the fluid inone direction or another.

As shown in FIGS. 32-36 , elliptical microtubes 2050 can be used in flowpersuasion, flow directing, or flow biasing to control the direction ofthe flow of the fluid 2007 on the outside of the heat exchanger 2010.For example, the angle of orientation of each new column of microtubes2050 may be offset by an additional five degrees as shown in FIGS. 35-36, where column of microtubes 2050 a is flat, column of microtubes 2050 bis angled up at 5 degrees, column of microtubes 2050 c is angled up at10 degrees, and so on through column of microtubes 20501. In thisconfiguration, flow of fluid over the microtube heat exchanger, as shownin FIG. 34 , will be directed, biased or persuaded in a specificdirection. In some examples, such an arrangement of microtubes can beused to have a heat exchanger that must fit a certain footprint butwhere the flow of the fluid on the outside of the heat exchanger isdirected in an orientation that is not strictly normal to the heatexchanger.

In yet other examples, as shown in FIG. 37 , the flow of the fluid 2107on the outside of the heat exchanger 2110 can be directed in multipledirections by microtubes 2150 having oval cross-sections, for examplegradually upward and then gradually back in a normal direction. As willbe understood based on this presentation of the technology, anyarrangement of the direction of flow of external fluid that wouldotherwise be normal to the flow of internal fluid can be achievedthrough such an arrangement of the array of microtubes.

FIGS. 38-39 show an array of microtubes 2250 for a heat exchanger core2210 having square cross-sectional shapes according to some aspects ofthe present technology. The microtubes 2250 may be arranged in eitheraligned arrangements (not shown) or staggered arrangements as shown inFIGS. 24-25 . The arrangement of microtubes having a square shape may beused to direct airflow over the heat exchanger. For example, in someembodiments, the square shape and the ratios of the cross-sectional sizeto the spacing may be selected to produce the desired air flow acrossthe heat exchanger. In some embodiments, the square cross section may beused to slow the flow of the exterior fluid according to the heattransfer needs of a particular application. In yet other examples, themicrotubes may be angled, as discussed with reference to FIGS. 32-37 ,to direct or bias the flow of the exterior fluid into certain paths.

FIGS. 40 a-c depict another microtube heat exchanger 2310 according toaspects of the technology that include a multi-pass or cross-flowconfiguration. A shield, fin, or blocking plate 2345 is positioned inthe heat exchanger to force the exterior fluid 2307 into a torturouspath of flow. For example, a single blocking plate 2345 may extendpartially through the center of the heat exchanger, parallel to themicrotubes. The exterior fluid may enter on one side of the blockingplate 2307 a and the plate will prevent the exterior fluid from flowingto the other side of the blocking plate until it has travelled throughthe desired path, around the blocking plate, and exiting the heatexchanger core on the opposite site of the blocking plate 2307 b. Inother examples, the blocking plate may be used to direct the flow intoany desired path, and may include exiting the microtube heat exchangercore on the same side as the entrance, on the opposite side, or oneither end of the heat exchanger core.

In aspects of the technology, the cross flow or multi-pass configurationprovides the benefit of increased efficiency, especially for refrigerantstyle, liquid cross flow. Giving the cross flow more time, and makingsure it reaches all areas of the heat exchanger core, can significantlyincrease the heat exchange efficiency.

FIG. 41 shows yet another example of a multi-pass or cross flowconfiguration, where three blocking plates 2345 a, 2345 b, and 2345 care used to induce a torturous path of exterior flow 2307 through theheat exchanger core 2310. It will be understood that other variations ofblocking plates can be used to create any cross flow or multi-passdesired for any configuration.

FIGS. 42-43 depict microtube heat exchanger cores according to thepresent technology that include integrated foreign object debris orforeign object damage (FOD) protection. In some aspects of thetechnology, ram airflow is employed for heat exchange, as describedherein. Fans are not used to induce air flow, but rather the heatexchanger is placed in a portion of an aircraft, such as a scoop, whereair flows due to the travel of the aircraft. In such arrangements,foreign objects such as rocks, pebbles, birds or other floating orflying objects cause concern over FOD. Rather than employing a separateFOD shield, the heat exchanger of the present technology can be modifiedto include integrated FOD protection. For example, as shown in FIG. 42 ,a front row of tubes that face the free stream air can be thicker walledand or have a larger diameter. This robust front wall can act like ablockade for the FOD, while all the tubes behind the front wall aremaximum efficiency microtubes. In some aspects of the technology, therobust tubes can be hollow (FIG. 42 b ) to continue to provide some heatexchange, or can be solid (FIG. 43 b ) to provide a more robust barrierand to prevent any leakage within the system should FOD caused damage toa microtube. In yet other examples, the reinforced microtube could havethe same diameter as the remaining microtubes, while having a thickerwall, and consequently thinner opening.

With specific reference to FIGS. 42 a-b , a microtube heat exchangercore 2410 includes a first end plate 2420 and a second end plate 2430,each with an array of openings 2425. A corresponding array of microtubes2450 are arranged and inserted into the array of openings 2425. Forsimplicity, only a small number of openings and microtubes are shown,while in application, the microtubes and openings would be much greaterin number and much closer together. The microtubes may include standardmicrotubes 2450 as discussed herein, and reinforced microtubes 2452 forFOD protection. The reinforced microtubes 2452 may include microtubes ofa larger diameter and a greater thickness that provide the requiredstrength for FOD protection.

With specific references to FIGS. 43 a-c , a microtube heat exchangercore 2510 includes a first end plate 2520 and a second end plate 2530,each with an array of openings 2525. A corresponding array of microtubes2550 are arranged and inserted into the array of openings 2525. Forsimplicity, only a small number of openings and microtubes are shown,while in application, the microtubes and openings would be much greaterin number and much closer together. The microtubes may include standardmicrotubes 2550 as discussed herein, and reinforced microtubes 2552 forFOD protection. The reinforced microtubes 2552 can include microtubeshaving the same diameter as standard microtubes 2550, but that aresolid, or do not have any opening within the microtube. The solidmicrotubes 2552 increase the strength and resistance to damage from FOD.In the event that FOD causes any damage to the solid microtubes 2552, aleak path of fluid within the microtube heat exchanger core is notcreated because fluid does not flow through microtubes 2552.

Though FIGS. 42-43 depict a single line of microtubes being reinforcedfor FOD protection, it will be understood that other arrangements arecontemplated by the present disclosure. For example, in any array ofmicrotubes for a given heat exchanger core, all of the outermostmicrotubes may be reinforced, either with larger diameter, hollowmicrotubes 2452, with rods or solid tubes 2552, or with any other typeof reinforced microtube. If the array is square, not only the leadingedge, but all other edges of microtubes would be reinforced. Similarly,in a circular array of microtubes, each of the outside microtubes couldbe reinforced.

In accordance with one aspect of the technology, a method of providingheat transfer in an aerospace application is disclosed. The methodincludes providing two end plates with an array of openings, providing amicrotube for each of the openings, each microtube laser welded to thecorresponding opening, and placing the microtubes and end plates in avapor cycle system for an aerospace application. In one aspect of themethod, a first fluid flows through the inside of the microtubes and asecond fluid flows over the outside of the microtubes. The method caninclude the microtubes forming one of a cylinder, rectangle, square orhorse shoe shape when laser welded to the array of openings.

In aspects of the technology, the method can include arranging themicrotubes in an array that forms straight longitudinal rows parallel tothe direction of fluid flow and straight transverse rows normal to thedirection of fluid flow. In yet other methods, the array of microtubesforms staggered longitudinal and transverse rows.

In some aspects, the configuration of the microtubes can be consideredrows and columns of microtubes. For example, a heat exchanger may have10 rows of microtubes formed in 100 columns to create a rectangular heatexchanger. Any number of rows and columns may be used to form any shapedesired. In yet other embodiments, the array of holes in the end platesmay be configured to reduce the surface area of the end plate byavoiding strictly linear columns and rows, as depicted herein.

In other aspects of the technology, the present technology also relatesto a method for manufacturing microtube heat exchangers. The aerospaceindustry, as technology improves, has created situations in which amicrotube style heat exchanger would solve heating problems.Traditionally, a method of laser welding an array of microtubes of thesizes discussed herein has not existed. Moreover, a method of accountingfor growth based on a first weld before welding a second weld, such thatthe array's accurately welded tube count is at a desirable level, hasnot existed.

To solve the issue of laser weld accuracy, the present technologyincludes the method of using a cnc laser path program in conjunctionwith a cnc vision system to account for the thermal growth within themetal being welded that will create errors in the positions of the arrayof welds. This present technology thus allows the microtube “successfulweld” rate within an array of hundreds or more microtubes to increasefrom the range of 90% to a range around 99%.

According to aspects of the technology, a method of manufacturing amicrotube heat exchanger includes providing two end plates with an arrayof openings, providing a microtube for each of the openings, using a cnclaser welder to weld a path around the microtubes within the openings,using a cnc vision system to account for the thermal growth within themetal being welded. In aspects, the weld path of a second microtube isadapted or changed based on the thermal growth caused by welding a firstmicrotube.

The foregoing detailed description describes the technology withreference to specific exemplary aspects. However, it will be appreciatedthat various modifications and changes can be made without departingfrom the scope of the present technology as set forth in the appendedclaims. The detailed description and accompanying drawings are to beregarded as merely illustrative, rather than as restrictive, and allsuch modifications, combination of features, or changes, if any, areintended to fall within the scope of the present technology as describedand set forth herein. In addition, while specific features are shown ordescribed as used in connection with particular aspects of thetechnology, it is understood that different features may be combined andused with different aspects. By way of example only, the microtube heatexchanger may be used with any combination of components in anEnvironmental control system for aircraft, and may also be used with anynumber of other components in another aspect of the technology.Likewise, numerous features from various aspects of the technologydescribed herein may be combined in any number of variations as suits aparticular purpose.

More specifically, while illustrative exemplary aspects of thetechnology have been described herein, the present technology is notlimited to these aspects, but includes any and all aspects havingmodifications, omissions, combinations (e.g., of aspects across variousembodiments), adaptations and/or alterations as would be appreciated bythose in the art based on the foregoing detailed description. Thelimitations in the claims are to be interpreted broadly based on thelanguage employed in the claims and not limited to examples described inthe foregoing detailed description or during the prosecution of theapplication, which examples are to be construed as non-exclusive. Forexample, with reference to the present technology, the term “preferably”is non-exclusive where it is intended to mean “preferably, but notlimited to.” Any steps recited in any method or process claims may beexecuted in any order and are not limited to the order presented in theclaims. Means-plus-function or step-plus-function limitations will onlybe employed where for a specific claim limitation all of the followingconditions are present in that limitation: a) “means for” or “step for”is expressly recited; and b) a corresponding function is expresslyrecited. The structure, material or acts that support themeans-plus-function are expressly recited in the description herein.Accordingly, the scope of the technology should be determined solely bythe appended claims and their legal equivalents, rather than by thedescriptions and examples given above.

The invention claimed is:
 1. A microtube heat exchanger of anenvironmental control system (ECS) of an aircraft, the microtube heatexchanger comprising: a first and a second end plate, wherein each endplate comprises a plurality of openings, the first end plate is coupledwith a coolant fluid return line of the ECS, and the second end plate iscoupled with a coolant fluid supply line of the ECS; and a plurality ofmicrotubes disposed between the first and second end plates, each of theplurality of microtubes aligned with corresponding openings of the firstand second end plate and configured to transfer coolant fluid betweenthe first and second end plates, wherein each of the plurality ofmicrotubes is laser welded to the first and second end plates.
 2. Themicrotube heat exchanger of claim 1, wherein the microtube heatexchanger is disposed in RAM air system of the aircraft such that thecoolant fluid transferred by the plurality of microtubes is configuredto be cooled by RAM air flowing past an exterior of the plurality ofmicrotubes.
 3. The microtube heat exchanger of claim 2, furthercomprising a mid-plate disposed between the first and second end platesand angled to direct the direction of flow of RAM air flowing past theexterior of the plurality of microtubes.
 4. The microtube heat exchangerof claim 2, wherein a portion of the plurality of microtube arereinforced microtubes and the rest of the plurality of microtubes areregular microtubes.
 5. The microtube heat exchanger of claim 4, whereina diameter of each of the reinforced microtubes is greater than adiameter of each of the regular microtubes.
 6. The microtube heatexchanger of claim 4, wherein a wall thickness of each of the reinforcedmicrotubes is greater than a wall thickness of each of the regularmicrotubes.
 7. The microtube heat exchanger of claim 4, wherein thereinforced microtubes are disposed on an air inlet side of the microtubeheat exchanger and are configured to protect the regular microtubes fromforeign object debris.
 8. The microtube heat exchanger of claim 1,wherein the plurality of microtubes form an arc.
 9. The microtube heatexchanger of claim 1, wherein the plurality of microtubes form a curve.10. The microtube heat exchanger of claim 1, wherein the plurality ofmicrotubes are arranged in a generally U-shaped formation to at leastpartially surround a cooling fan of the ECS.
 11. A RAM air scoopassembly for an aircraft, comprising: an inlet through which RAM airenters the RAM air scoop assembly; a duct disposed downstream of theinlet; and a microtube heat exchanger of an environmental control system(ECS) of the aircraft, the microtube heat exchanger disposed within theduct and comprising: a first end plate and a second end plate coupled toopposing sides of the duct, wherein each end plate comprises a pluralityof openings, the first end plate is coupled with a coolant fluid returnline of the ECS, and the second end plate is coupled with a coolantfluid supply line of the ECS, and a plurality of microtubes disposedbetween the first and second end plates, each of the plurality ofmicrotubes aligned with corresponding openings of the first and secondend plate and configured to transfer coolant fluid between the first andsecond end plates, wherein each of the plurality of microtubes is laserwelded to the first and second end plates, wherein the microtube heatexchanger is disposed in the duct such that the coolant fluidtransferred by the plurality of microtubes is configured to be cooled byRAM air flowing past an exterior of the plurality of microtubes.
 12. TheRAM air scoop assembly of claim 11, further comprising a mid-platedisposed between the first and second end plates and angled to directthe direction of flow of the RAM air flowing past the exterior of theplurality of microtubes.
 13. The RAM air scoop assembly of claim 11,wherein a portion of the plurality of microtube are reinforcedmicrotubes and the rest of the plurality of microtubes are regularmicrotubes.
 14. The RAM air scoop assembly of claim 13, wherein adiameter of each of the reinforced microtubes is greater than a diameterof the regular microtubes.
 15. The RAM air scoop assembly of claim 13,wherein a wall thickness of each of the reinforced microtubes is greaterthan a wall thickness of each of the regular microtubes.
 16. The RAM airscoop assembly of claim 13, wherein the reinforced microtubes aredisposed on an air inlet side of the microtube heat exchanger areconfigured to protect the regular microtubes from foreign object debris.17. The RAM air scoop assembly of claim 11, wherein the plurality ofmicrotubes form an arc.
 18. The RAM air scoop assembly of claim 11,wherein the plurality of microtubes form a curve.
 19. The RAM air scoopassembly of claim 11, wherein: each of the plurality of microtubes has asame microtube diameter; the plurality of microtubes are formed inlongitudinal and transverse rows and have uniform spacing between eachother in the longitudinal and transverse direction; a ratio between themicrotube diameter and a longitudinal distance between the centers oftwo adjacent microtubes is 1.25; and a ratio between the microtubediameter and a transvers distance between the centers of two adjacentmicrotubes is 2.75.
 20. The RAM air scoop assembly of claim 11, wherein:each of the plurality of microtubes has a same microtube diameter; theplurality of microtubes are formed in staggered longitudinal andtransverse rows and have uniform spacing between each other in thelongitudinal and transverse direction; a ratio between the microtubediameter and a longitudinal distance between the centers of two adjacentmicrotubes is 1.3; and a ratio between the microtube diameter and atransvers distance between the centers of two adjacent microtubes is1.5.